Wang Z.,AMEC Environment and Infrastructure Inc.
Geotechnical Special Publication | Year: 2013
It is well established that soils exhibit non-linear behavior even at small strain levels. Yet, most evaluations of the seismic response of soil deposits utilize an equivalent linear methodology, i.e. elastic solutions incorporating constant damping. In such solutions the modulus and damping constants are adjusted by means of an iterative approach to correlate to the maximum strain. In doing so, the smaller amplitude, high-frequency component motions are forced to use the same modulus degradation and damping as that of the lower frequency motions. As a consequence, the computed motions at the surface of a deposit often exhibit unrealistic low amplitudes at high frequencies when the strong input motions are applied. This article presents a modified Kelvin model, in which the modulus and damping are treated as loading history dependent coefficients for each loading-unloading branch. This model works in the program FLAC in a time domain integration procedure. Based on the peak strain level experienced in the previous half cycle, the modulus degradation and viscosity are updated for the current branch. Numerical analyses for a soft soil site are presented and compared with those obtained using the equivalent linear method implemented in the program SHAKE for a recorded motion at Treasure Island. The site response analysis of another soft clay site for a higher design input motion shows that the computed PGA and response spectral could be higher than those obtained from a typical equivalent linear analysis. © 2013 American Society of Civil Engineers.
Youngs R.R.,AMEC Environment and Infrastructure Inc.
Earthquake Spectra | Year: 2014
We present an update to our 2008 NGA model for predicting horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The update is based on analysis of the greatly expanded NGA-West2 ground motion database and numerical simulations. The updated model contains minor adjustments to our 2008 functional form related to style of faulting effects, hanging wall effects, scaling with the depth to top of rupture, scaling with sediment thickness, and the inclusion of additional terms for the effects of fault dip and rupture directivity. In addition, we incorporate regional differences in far-source distance attenuation and site effects between California and other active tectonic regions. Compared to our 2008 NGA model, the predicted medians by the updated model are similar for M > 7 and are lower for M < 5. The aleatory variability is larger than that obtained in our 2008 model. © 2014, Earthquake Engineering Research Institute.
Hansen S.,AMEC Environment and Infrastructure Inc |
Beukema P.,Environment Canada
ICSI 2014: Creating Infrastructure for a Sustainable World - Proceedings of the 2014 International Conference on Sustainable Infrastructure | Year: 2014
We cannot simply "flip the switch" and move from fossil fuel-based power to renewable power as many would like to believe. Sustainability is an evolution not a revolution. The global community has developed a reliance on fossil fuels and many other nonrenewable commodities, including precious metals and other minerals provided by the earth. These natural resources are enablers in today's society in that they are necessary to fuel our lifestyle and quality of life. Globally, the result is a continued depletion of natural resources, thus, if not arguably, increasingly affecting our ability as a society to ensure the availability of natural resources for future generations. Therefore, while we continue to consume natural resources we have to hope and anticipate that our future generations will continually evolve sustainably. Businesses drive the world economy, and whereas governments can pass legislation for standards and requirements, ethical behavior cannot be legislated. However, it is clear that once unethical behavior is uncovered, the consequences to an organization for its unethical behavior can be severe, but by then the damage is already done and difficult, if not impossible, to undo. The Code of Ethics that a business adopts determines and shapes its ethical practices and it is the resulting culture and attitudes of its employees that maintain its reputation. Although founded in common principles, each business will adopt a unique ethical code. Arguably, it is, at least in part, through the ethical decisions that engineering companies achieve the Social License to Operate (SLO) that drives sustainable development locally, regionally, and globally. In this paper we take a look at ethics and the social license that businesses, specifically engineering companies, are adopting to guide the sustainability evolution and the consequences (intended and unintended) of those paths. © 2014 American Society of Civil Engineers.
Hall S.J.,Arizona State University |
Trujillo J.,U.S. Environmental Protection Agency |
Nakase D.,Arizona State University |
Strawhacker C.,Native Seed SEARCH |
And 3 more authors.
Ecosystems | Year: 2013
Closely integrated research between archaeologists and ecologists provides a long-term view of human land use that is rare in the ecological literature, allowing for investigation of activities that lead to enduring environmental outcomes. This extended temporal perspective is particularly important in aridlands where succession occurs slowly and ecosystem processes are mediated by abiotic, geomorphic factors. Numerous studies show that impacts from ancient human actions can persist, but few have explored the types of practices or mechanisms that lead to either transient or long-term environmental change. We compared plant and soil properties and processes from a range of landscape patch types in the Sonoran Desert of the US Southwest that supported different, well-documented prehistoric farming practices from AD 750-1300. Our results show that the types of ancient human activities that leave long-term ecological legacies in aridlands are those that fundamentally alter "slow variables" such as soil properties that regulate the timing and supply of water. Prehistoric Hohokam floodwater-irrigation practices, but not dryland farming techniques, substantially altered soil texture, which was strongly associated with desert plant community and functional composition. However, prehistoric agriculture did not consistently alter long-term nutrient availability and thus had no impact on "fast variables" such as production of seasonal annual plants that are restricted to periods of ample rainfall. In this arid ecosystem, the inverse texture model explained patterns in plant functional composition at large scales, but is less predictive of production of short-lived desert annuals that experience a more mesic precipitation regime. © 2013 Springer Science+Business Media New York.
Lommler J.C.,AMEC Environment and Infrastructure Inc |
Bandini P.,New Mexico State University
Geotechnical Special Publication | Year: 2015
Collapsible soils are generally considered to be soils that settle upon wetting and loading. Settlement of collapsible soils is a common problem particularly in arid and semi-arid regions of the United States because these soils exist at very low moisture contents in their natural environment. Locally, geotechnical engineers refer to native soils that settle due to self-weight upon wetting as "collapsible soils" or "hydro-collapsible soils." This paper presents some observations and findings of a study on natural collapsible granular soils that formed in alluvial fans in central New Mexico. The paper describes the soil structure observed in microphotographs and scanning electron microscope images and the effects of sample disturbance on the prediction of soil collapse upon wetting from laboratory test results. The paper offers a hypothesis on the mechanism that could have produced some features of the structure of the collapsible soils in the area. © ASCE 2015.
Zhang M.,Seattle University |
Wentworth T.D.,AMEC Environment and Infrastructure Inc.
Geotechnical Special Publication | Year: 2014
This paper presents a case study of the use of underground injection control (UIC) wells to infiltrate stormwater beneath relatively impermeable near-surface soils at an elementary school. Stormwater had previously been routed to a central pipe and discharged to a ravine on an adjacent property, causing severe erosion. UIC wells were used to infiltrate stormwater into the subsurface beneath impermeable shallow soils to prevent such erosion and to comply with current stormwater regulations. The UIC well system consists of more than 50 UIC wells, each of which is 1 meter in diameter and 18 to 24 meters deep. Water-quality treatment is provided by catch basin dead storage and filters. Short-term pilot infiltration tests and three-dimensional numerical modeling of variably saturated flow were used to develop design infiltration rates and radii of influence for UIC wells. Infiltration testing on completed UIC wells helped address variable geological conditions during construction. The success of this sustainable stormwater drainage system was a result of favorable geological conditions, comprehensive design studies, a thorough site investigation, pilot testing, numerical modeling, and field verification testing during construction. UIC wells can work well at sites with limited space and a thick unsaturated zone. © 2014 American Society of Civil Engineers.
Bierman P.R.,University of Vermont |
Coppersmith R.,Coppersmith Consultingm Inc. |
Hanson K.,AMEC Environment and Infrastructure Inc |
Neveling J.,Council for Geoscience |
And 5 more authors.
GSA Today | Year: 2014
Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10Be in river sediment samples and found that south-central South Africa is eroding ∼5 m m.y.-1, a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10Be and 26Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of <0.2 m m.y.-1 (median, 0.34 m m.y.-1), consistent with no Quaternary movement on faults that displace the underlying quartzite but not the silcrete cover. We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known.
Honeycutt J.N.,GRL Engineers Inc. |
Kiser S.E.,AMEC Environment and Infrastructure Inc. |
Anderson J.B.,Auburn University
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014
This study examined the energy transfer ratio (ETR) of Central Mine Equipment (CME) automatic standard penetration test (SPT) hammers utilizing a large database of SPT energy measurements. The database consisted of energy measurements from 17,825 SPT hammer blows obtained from 33 CME automatic hammers over a 5-year period, many of which were tested multiple times. The average ETR for all 17,825 CME automatic hammer blows in the database was 82.9% with a COV of ±7:4%. The database also provided an opportunity to determine the impacts of hammer calibration, test depth, and calibration interval on the measured ETR. The impact on average ETR of eliminating hammer blows due to D4633-10 restrictions was also demonstrated. © 2014 American Society of Civil Engineers.
Fletcher K.,The Game and Wildlife Conservation Trust |
Howarth D.,The Game and Wildlife Conservation Trust |
Kirby A.,The Game and Wildlife Conservation Trust |
Kirby A.,AMEC Environment and Infrastructure Ltd |
And 3 more authors.
Ibis | Year: 2013
Upland birds are predicted to be particularly vulnerable to the effects of climate change, yet few studies have examined these effects on their breeding phenology and productivity. Laying dates of Red Grouse Lagopus lagopus scotica in the Scottish Highlands advanced by 0.5 days/year between 1992 and 2011 and were inversely correlated with pre-laying temperature, with a near-significant increase in temperature over this period. Earlier clutches were larger and chick survival was greater in earlier nesting attempts. However, chick survival was also higher in years with lower May temperatures and lower August temperatures in the previous year, the latter probably related to prey abundance in the subsequent breeding season. Although laying dates are advancing, climate change does not currently appear to be having an overall effect on chick survival of Red Grouse within the climate range recorded in this study. © 2013 British Ornithologists' Union.
Johnson S.R.,AMEC Environment and Infrastructure Inc. |
Johnson S.R.,North Carolina State University |
Burchell M.R.,North Carolina State University |
Evans R.O.,North Carolina State University |
And 2 more authors.
Ecological Engineering | Year: 2013
Relatively narrow (<50m) riparian buffers strategically reestablished in correct landscape positions have been shown to significantly reduce agricultural non-point source pollution to streams. Because of this, conservation programs have been established to encourage landowners to enroll lands near surface waters to improve water quality. Former cropland enrolled in a conservation program was evaluated to determine its effectiveness in reducing nitrate-nitrogen (NO3--N) in shallow groundwater. This conservation buffer (CB) was up to 80m wide and was planted with loblolly pine (Pinus taeda). It was situated upslope of an existing 30-60m wide riparian hardwood forest buffer (EHB) located within the floodplain of an intermittent stream. Shallow groundwater NO3--N, groundwater hydrology, total organic carbon, and soil redox potential were measured throughout both the CB and the EHB for 18 months. Groundwater NO3--N concentrations, often 5-15mgL-1 within the CB, were not significantly reduced from concentrations that entered from the agricultural field edge. However, a decrease in NO3--N concentration was observed within the EHB (17-83%). The hydrology of the CB coupled with relatively low organic carbon contributed to a low denitrification potential and lack of NO3--N reduction compared with the EHB. While the CB enrollment likely provided additional habitat benefits it did not appear to provide treatment of groundwater NO3--N. It is our conclusion that landscape position is a more important defining variable for buffer site selection than buffer width if NO3--N reduction is a primary goal. © 2012 Elsevier B.V.